The One-Bowl Cookie Bars All My Friends Beg Me to Bake

• 1 Egg, large

• 1 1/4 cups All-purpose flour

• 1/2 tsp Baking powder

• 1 cup Brown sugar, packed light

• 1/4 tsp Kosher salt

• 1 cup Or bittersweet chocolate chips, white semisweet

• 1/4 tsp Salt, flaky

• 1 tsp Vanilla extract

• 8 tbsp Butter, unsalted